An important factor in the raising of rice seedlings, in which young plants that are susceptible to environmental changes or diseases and pests, are grown together under management, and seedlings that have grown to a certain extent are planted in the field, is to produce seedlings that are excellent in the growth of roots, stem thickness, dry weight and the degree of sturdiness (dry weight/height) and have a seedling height (or an internode) of an appropriate length.
Many agents for improving the growth of rice seedlings have been hitherto investigated. Hydroxyisoxazoles are known to have an effect of promoting root growth, and are thus used in the raising of healthy seedlings (Patent Document 1). Furthermore, there have been reports on the effect of seedling growth exerted by jasmonic acid, which is a plant hormone (Patent Document 2); the effect of seedling growth obtained by preventing turion formation using uniconazole P, which is a gibberellin biosynthesis inhibitor (Non-Patent Document 1); and the like.
However, these agents for improving the growth of the seedlings are still not fully satisfactory.
Meanwhile, 5-aminolevulinic acid, derivatives thereof, or salts of the acid or the derivatives exhibit an enhancement of photosynthetic activity, an enhancement of CO2 absorption capability, an action of suppressing respiration, an action of enhancing the chlorophyll content, and also an excellent action of promoting growth. As a result, the compounds are known to show excellent effects in the promotion of root generation, prevention of lodging, increase of the yield, enhancement of cold hardiness, retainment of freshness, enhancement of greenness, retainment of greenness, raising of healthy seedlings, promotion of organ development, increase of the tillering number, shortening of the time period required for growth, alleviation of harmful side effects of chemicals, or increase of survival upon cutting and the like (Patent Document 3).
Furthermore, it has reported that when a young sugar beet plant is treated with uniconazole P, which is a gibberellin biosynthesis inhibitor, and then is treated with 5-aminolevulinic acid, a derivative thereof or a salt thereof, the growth of sugar beet can be induced (Non-Patent Document 2). This is a technology dealing with the problem that growth stagnation of sugar beet occurs, which means a decrease in the dry weight of sugar beet, as a result of sustainment of the effect of uniconazole P used for preventing turion formation, and solving the problem by increasing the dry weight due to the growth promoting effect of 5-aminolevulinic acid and returning to healthy growth, by treating sugar beet with 5-aminolevulinic acid 15 days after treatment with uniconazole P.
However, what becomes potent when uniconazole P and 5-aminolevulinic acid are used in combination, is the effect of preventing lodging of young sugar beet plants, which results from the summation of the effect of the gibberellin biosynthesis inhibitor inducing the suppression of internode elongation, and the effect of 5-aminolevulinic acid inducing repletion of roots and stems, and the growth effect of the seedlings is still not fully satisfactory.
Patent Document 1: JP-A-60-52048
Patent Document 2: JP-A-10-310580
Patent Document 3: JP-A-4-338305
Non-Patent Document 1: “Growth of Healthy Seedlings Using Uniconazole P Liquid Preparation”, Technology transferred with dissemination in year 2005, Fukui-ken
Non-Patent Document 2: “Effect of Fertilizer Containing 5-Aminolevulinic Acid on Delay of Growth Due to Uniconazole Treatment”, Proceedings of the Japanese Society for Chemical Regulation of Plants, No. 38, p. 71